The present invention relates to a device and method for network interoperability between fully IP communications networks or sub-networks or networks that use IP for communication either fully or partially, and, more particularly, but not exclusively to providing communications networks around the world with interconnectivity even when there are no business relations between the respective networks.
The concept of a roaming broker has been proven in the GSM world by the existence of several GSM roaming brokers. Some of them have been initiated by the GSMA, the GSM association. The need for a roaming broker is caused mainly by the fact that new & small operators do not have the time and resources to sign roaming agreements with many existing operators in order to serve the needs of their outbound roamers, or that the large operators do not have resources to sign roaming agreements with the new small operators. International Patent Application No. WO9955107 to Swisscom addresses such roaming brokers, and in particular issues such as how mobile identities from a non-recognized network can obtain roaming registrations by switching the roamer's home network identity to a broker's identity which is recognized by the roaming network.
In the next generation of communications, the issue is expected to be much more extensive and no longer restricted to roaming or to mobile telephones. Next generation communications networks are expected to be based on Internet protocol (IP). Not only will there be more mobile networks but such interworking issues may apply to fixed line and cable networks which wish to place calls with any other network in the world. Furthermore there will be large numbers of smaller networks, say from the WiFi/WiMAX arena. Operators of WiFi/WIMAX network, ranging from citywide to hotspot type networks will also want to provide their users with full connectivity, and it will be impossible for every small hotspot operator to be included in full interworking agreements. Thus there will be IMS (IP Multimedia Sub-system) players and also fixed-line and cables network operators requiring interworking, but their sheer numbers will make full interworking impractical.
Long term evolution (LTE) refers to standards for a fourth generation of mobile telephony 4G. LTE calls for a theoretical capacity of up to 100 Mbit/s in the downlink and 50 Mbit/s in the uplink. Most major mobile carriers in the United States and several worldwide carriers have announced plans to convert their networks to LTE, and the world's first publicly available LTE-service was opened in the two Scandinavian capitals Stockholm and Oslo on the 14 Dec. 2009, and branded 4G. The physical radio interface was at an early stage named High Speed OFDM Packet Access (HSOPA), now named Evolved UMTS Terrestrial Radio Access (E-UTRA).
Next Generation Networks (NGN), may include LTE as the infrastructure that replaces the current GPRS layer. IMS, discussed in greater detail below, may be layered on top of an LTE layer, but not necessarily. One may have LTE alone, without IMS. An alternative is to have IMS alone, on top of GPRS, without LTE. In LTE, the relevant network components are the MME which is discussed below and which functions like the VLR in the legacy GSM network. Another component is the home subscriber server or HSS, which has shared functionality with the HLR of the GSM network. In LTE Roaming, the MME sends a registration request for a new inbound roaming user to the home HSS. The protocol used is Diameter, by contrast with the legacy GPRS network, where MAP is used, and in addition to the IMS registration where SIP is used.
The IP Multimedia Subsystem (IMS) is an architectural framework for delivering Internet Protocol (IP) multimedia services. It was originally designed by standard bodies such as the 3GPP, the 3rd Generation Partnership Project, as a part of the vision for evolving mobile networks beyond GSM. Its original formulation (3GPP R5) represented an approach to delivering “Internet services” over the general packet radio service (GPRS). This vision was later updated by 3GPP, 3GPP2 and TISPAN by requiring support of networks other than GPRS, such as Wireless LAN, CDMA2000 and fixed line.
To ease the integration with the Internet, IMS uses Internet Engineering task force (IETF) protocols wherever possible, e.g. Session Initiation Protocol (SIP). IMS intends to aid the access of multimedia and voice applications from wireless and wireline terminals, i.e. create a form of Fixed Mobile Convergence (FMC). This is done by having a horizontal control layer that isolates the access network from the service layer.
At the moment, the interworking issue arises mainly with cellular networks and with roaming, since the roaming telephone has to register with its home network before the call is allowed. The issue is not critical where PSTN is involved since fixed line phones do not roam but also because international telephone connections often manage to lose their source information, the CLI, over the international connections, so that the receiving network does not know where the call originates from. Thus today, International calls can often be placed between two countries that are in a state of war, since the receiving network does not know the call's origin. However the IP protocol preserves the source information and thus the problem will start to be an important one for fixed line networks.
Another issue is the appearance of the virtual operator. There already exist telephone operators who do not own any switches or wires. They simply buy telephone time wholesale at a discount from a wireline operator and sell the time on to their customers. The emergence of mobile virtual network operators (MVNOs), who do not have base stations or spectrum of their own but buy time wholesale is also expected. In fact the wireline operators themselves may establish MVNOs and increase the number of mobile operators and hence the roaming capabilities. The need for each pair of mobile operators to sign a roaming agreement imposes a difficult enough restriction, but when this is extended to interworking between networks overall, and when the expected mass IMS deployment takes place, it is clear that one-to-one agreements will not be feasible.
That is to say, interworking is not needed only for the case of roaming, where a roaming subscriber is involved, but also in the case of international interoperability between IMS networks which do not have direct relations. In IMS, in order for a session to go directly from network A to network B, both networks may be expected to have bi-lateral agreements.
One possible option would be to use an international carrier. But such an international carrier would have to emulate an IMS network as well. Therefore the same interoperability issues may apply to the International carrier.